I don't think you can do it seamlessly - had you knitted one section and then when starting the second section you could have picked up stitches along the edge and knit the next square, but you still would have had a seam - the seam would be smaller than if sewn, but still a seam. I think you are going to have to sew them together.
OTN - lacy sweater and just beginning another pair of socks - toe up
FO's: garterstitch scarf, dropped stitch cable fingerless mittens, socks for Christmas, and 6 baby hats, cabled toddler hat, hat for mom, MIL socks
My blog: http://knitquiltmom.blogspot.com/
I'm knitquiltmom on Ravelry... I'm slowly loading my projects. I also have several patterns that are being offered as free downloads.